LP2989LV_15 Datasheet, PDF (16/26 Pages) Texas Instruments – Micropower and Low-Noise, 500-mA Ultra Low-Dropout Regulator for Use With Ceramic Output Capacitors

LP2989LV
SNVS086K – MAY 2000 – REVISED JULY 2015
10 Layout
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10.1 Layout Guidelines
For best overall performance, place all circuit components on the same side of the circuit board and as near as
practical to the respective LDO pin connections. Place ground return connections to the input and output
capacitor, and to the LDO ground pin as close to each other as possible, connected by a wide, component-side,
copper surface. The use of vias and long traces to create LDO circuit connections is strongly discouraged and
negatively affects system performance. This grounding and layout scheme minimizes inductive parasitics, and
thereby reduces load-current transients, minimizes noise, and increases circuit stability. A ground reference
plane is also recommended and is either embedded in the PCB itself or located on the bottom side of the PCB
opposite the components. This reference plane serves to assure accuracy of the output voltage, shield noise,
and behaves similarly to a thermal plane to spread (or sink) heat from the LDO device. In most applications, this
ground plane is necessary to meet thermal requirements.
10.2 Layout Example
Input
Capacitor
VIN
BYPASS
N/C
GROUND
IN
Ground
SHUTDOWN
ERROR
Error Pullup
Resistor
VOUT
SENSE
OUT
VOUT
Output
Capacitor
Figure 16. LP2989LV Layout Example
10.2.1 Thermal Considerations
CAUTION
Due to the limited power dissipation characteristics of the available SOIC (D) and
WSON (NGN) packages, all possible combinations of output current (IOUT), input
voltage (VIN), and ambient temperatures (TA) cannot be ensured.
Power dissipation, PD is calculated from the following formula:
P_D = ((V_IN – V_OUT) × I_OUT)
(1)
The LP2989LV regulator has internal thermal limiting designed to protect the device during overload conditions.
For continuous normal conditions, the recommended maximum operating junction temperature is 125°C. It is
important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional
heat sources mounted nearby must also be considered.
For surface-mount devices, heat sinking is accomplished by using the heat-spreading capabilities of the PC
board and its copper traces. Copper board stiffeners and plated through-holes can also be used to spread the
heat generated by power devices.
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